When 9th District Congressman Bob Kasten vacated his seat to run for governor in 1978, Sensenbrenner ran in the election to succeed him, defeating his primary opponent, Susan Engeleiter, by 589 votes with a plurality of 43%.[5][6] He was elected in November 1978 with 61%,[7] and has been reelected 16 more times with no substantive opposition, sometimes running unopposed. His district was renumbered as the 5th after the 2000 census, when Wisconsin lost a district. He has never won re-election with less than 62% of the vote. In fact, his worst two re-elections were in 2004, when he defeated UW-Milwaukee professor Bryan Kennedy with 67% of the vote,[8] and in 2006 defeated him in a rematch with 62%.[9]

In 2005, Sensenbrenner authored the Real ID Act, which requires scrutiny of citizenship before issuing drivers' licenses to make it more difficult for terrorists and criminals to alter their identities by counterfeiting documents. He attached the controversial act as a rider on military spending bill HR418, which was passed by the Senate without debate.[12]

On June 17, 2005, Sensenbrenner, the chair of the House Judiciary Committee, ended a meeting where Republicans and Democrats were debating the renewal of the USA PATRIOT Act and walked out in response to Democratic members discussing human rights violations at the Guantanamo Bay detainment camp and the ongoing Iraq war. He ordered the court reporter to halt transcription of the proceedings and C-SPAN to shut off its cameras. Sensenbrenner defended his actions by stating that the Democrats and witnesses had violated House rules in discussing issues unrelated to the subject of the meeting.[13] Democrats have claimed that his walkout was contrary to House parliamentary procedure, which is to adjourn either on motion or without objection.[14]

In June 2013, Sensenbrenner objected to the FBI and NSA's use of the PATRIOT Act to routinely collect phone metadata from millions of Americans without any suspicion of wrongdoing. "The Bureau’s broad application for phone records was made under the so-called business records provision of the Act," he said. "I do not believe the broadly drafted FISA order is consistent with the requirements of the Patriot Act. Seizing phone records of millions of innocent people is excessive and un-American.”[15] He released a statement saying “While I believe the Patriot Act appropriately balanced national security concerns and civil rights, I have always worried about potential abuses.”[16][17]

He also criticized the PRISM program, stating that the Patriot Act did not authorize the program.[18][19]

Sensenbrenner supported the Amash Amendment, a plan to defund the NSA's telephone surveillance program. "Never, he said, did he intend to allow the wholesale vacuuming up of domestic phone records, nor did his legislation envision that data dragnets would go beyond specific targets of terrorism investigations." The Amendment fell seven votes short of the number it needed to pass.[20][21]

In October 2013, he introduced the USA Freedom Act in the House, a bill designed to curtail the powers of the NSA and end the NSA's dragnet phone data collection program. The bill is supported by civil liberties advocacy groups, including the American Civil Liberties Union.[22]

On September 8, 2005, Sensenbrenner voted against a bill to provide $50 billion in emergency aid to victims of Hurricane Katrina.[24] The bill passed and was signed into law by President George W. Bush.

In fall 2006, the Animal Fighting Prohibition Enforcement Act unanimously passed the Senate, but Sensenbrenner used his position to block final House consideration of the legislation, even though the bill had 324 co-sponsors. The act creates felony-level penalties for animal fighting activities.[citation needed]

Sensenbrenner was the only Republican to join House Speaker Nancy Pelosi's Congressional delegation to meet the Dalai Lama in Dharamsala, India during the March 2008 protests against China by Tibetans.[26] While there he said, "In the US Congress, there is no division between Democrats and Republicans on the issue of protecting Tibetan culture and eliminating repression against Tibetans around the world."[27]

Following the death of Nelson Mandela, Sensenbrenner objected to the executive proclamation by President Barack Obama to lower the flags to half-staff to honor Mandela. He stated it was his belief that the American flag should only be flown at half-staff for Americans.[28]

Sensenbrenner, in spite of unanimous Congressional support,[30] attempted to delay a bill[31] in December 2010 that would have been benefited Hotaru Ferschke, the Japanese-born widow of a United States Marine killed in combat. Congressman John Duncan were able to use "a loophole" to get the bill passed in spite of Sensenbrenner's objections. By adding language in the Senate indicating the bill would not impact the federal budget Sensenbrenner could no longer block the bill by himself according to House rules. The measure was passed unanimously.[32]

Sensenbrenner believes in criminal prosecution of broadcasters and cable operators who violate decency standards, in contrast to the FCC regulatory methods.[33] In July 2012, Sensenbrenner advocated amending the Espionage Act of 1917 to enable the prosecution of journalists involved in publishing leaks of state secrets.[34]

In December 2011, the Milwaukee Journal Sentinel reported Sensenbrenner referred to First LadyMichelle Obama’s “big butt” while talking to church members at a Christmas bazaar at St. Aidan's church in Hartford.[35] Church member Ann Marsh-Meigs told the newspaper that she heard Sensenbrenner’s remarks. She said the congressman was speaking about the first lady’s efforts to combat childhood obesity, and added, “And look at her big butt.” On December 22, Sensenbrenner’s press secretary said Sensenbrenner had sent Obama a personal note and released a statement saying he regretted his “inappropriate comment”. Sensenbrenner’s office would not release the text of the note.[36]

Sensenbrenner was named the 2006 "Man of the Year" by the conservative publication Human Events because of his opposition to open-borders immigration policies.[38] In contrast, in the same year he was rated the second-worst member of the House by Rolling Stone, which dubbed him "the dictator."[39] Also in 2006, the NRA lobbied Sensenbrenner to add a provision to the Patriot Act re-authorization that requires Senate confirmation of ATF director nominees.[11]

In 1977, Sensenbrenner married Cheryl Warren, daughter of former state attorney general and U.S. District Court Judge Robert W. Warren. The couple have two sons, Frank (born 1981), and Bob (born 1984). Frank worked as a lobbyist for the Canadian embassy in Washington D.C. starting in 2007, although he didn't register with the U.S. as an agent for a foreign government.[40] He is currently a Visiting Fellow at Johns Hopkins School of Advanced International Studies, his research focusing on Eurozone financial markets, and has blogged for the Huffington Post on Italian politics and the Vatican.[41][42]

Sensenbrenner has a net worth of about $11.6 million.[44] His net worth in 2010 was $9.9 million.[45] He is an heir to the Kimberly-Clark family fortune,[46] but no longer owns any Kimberly-Clark stock.[45] His great-grandfather, Frank J. Sensenbrenner, invented Kotex napkins and served as Kimberly-Clark's second president and CEO, but the congressman has never served on the board or been directly involved with the company.[45] He has put his money into stocks, as detailed in the Congressional Record.[6] Sensenbrenner has also won lottery prizes three times, the largest, $250,000, in 1998.[44][47]